Supported liquid membranes based on deep eutectic solvents for gas separation processes

Deep eutectic mixtures (DES) have been proposed in the last years as viable and more sustainable solvents, in a myriad of applications. CO₂ capture or adsorption is one of those possible applications, where DES can act as an alternative to the amine-based solvents that are currently being used in carbon capture and sequestration (CCS) processes. In this work, different choline chloride DES were prepared, and CO₂ solubility and diffusivity coefficients were measured. The DES were immobilized in a PTFE porous support, and the pure gas permeability of 3 different gases (N₂, CO₂ and CH₄) was assessed, as well as DES supported liquid membranes ideal selectivity. An enzyme that is able to convert CO₂ into bicarbonate was also added to the DES and DES supported membranes, in order to increase the transport towards CO₂. The tested DES show solubility values in line with the ones reported in literature for related DES family and ionic liquids. Solubility and diffusivity of CO₂ showed the best results in the DES composed of choline chloride and urea, showing even higher values when the enzyme was dispersed. The supported liquid membranes show higher permeability towards CO₂, especially in DES with choline chloride and urea. The membrane containing this DES also showed high selectivity for CO₂/CH₄, with values above the Robeson upper bound. This proves that DES supported membranes are a viable strategy for CO₂ adsorption/sequestration and that the prepared membranes may have applications in gas separation processes, particularly in the separation of CO₂ from CH₄, as in the case of natural gas streams treatment or biogas.